Ros printer incorporating a variable wavelength laser

Abstract

A fully electronic, nonmechanical raster output scanner (ROS) digital printer for high resolution xerographic printing is enabled by combining a laser adapted to produce a variable wavelength output with a dispersive element such as a grating to present a raster scan at an image plane. In a preferred embodiment, a diode laser is positioned within a laser cavity whose length is designed as a function of the resolution required for the scanned image. The wavelength varying output is incident upon a high resolution grating which diffracts the radiation through a diffraction angle which varies according to the wavelength of the incident light. A scan lens is positioned between the grating and a photoreceptor surface to provide focusing and scan linearity correction to the scan line.

What is claimed is: 
     
       1. A digital scanning laser printer for forming high resolution scan lines at a photosensitive image medium comprising: a broad-band wavelength tunable laser source operational in a plurality of longitudinal modes to provide a beam of radiation whose wavelength varies incrementally over the tunable range,   a high resolution diffraction grating in the path of said output radiation beam, wherein the radiation beam is incident to the grating at an angle α measured normal to the grating, said grating diffracting said output beam of radiation through an angle β the magnitude of β being determined by the wavelength of said beam of radiation, to produce an output beam which scans across a diffraction angle, and   a scan lens positioned between the photosensitive imaging medium and the grating, said scan lens focusing the diffracted beam onto the image medium as a linearized scan line comprising a plurality of neighboring pixels with uniform inter-pixel spacing corrected for distortion and spot size variations.   
     
     
       2. The printer of claim 1 wherein said laser source is operated within a resonator cavity, the cavity enclosing a medium with a characteristic index of refraction and the cavity having a length L given by the expression   L (nm)=λ.sup.2 /.sub.2n(FSR)     where   FSR is the value of the scan line inter-pixel spacing expressed in nm, n is the index of the resonator cavity medium and λ is the laser operating wavelength, in nm.   
     
     
       3. The printer of claim 1 wherein said grating is formed with a plurality of ruled, parallel lines, each line spaced apart by a distance d and wherein said grating diffracts said output beam of radiation into a plurality of beam orders according to the expression sin β=mλ/d-sin α where λ is the instant wavelength of the radiation beam and m is the order. 
     
     
       4. The printer of claim 1 wherein said laser source is a diode laser.